dispatchResize method
Implementation
void dispatchResize(
  Size newContentSize,
  Size newBorderSize,
) {
  if (!needResizeNotify(newContentSize, newBorderSize)) {
    return;
  }
  preContentSize = newContentSize;
  preBorderSize = newBorderSize;
  _dispatchResizeChange(ResizeObserverEntry(
      borderBoxSize: newBorderSize,
      contentBoxSize: newContentSize,
      devicePixelContentBoxSize: newContentSize,
      contentRect: newBorderSize));
}